There is ample evidence that tumors release antigen from the cell surface and that this antigen forms complexes with existing antibody in the circulation. The respective roles of free antigen, antigen-antibody complex, or free antibody have been demonstrated in vitro, although their interactions are not clear. The role of these same materials in the host immune response to tumors growing in vivo is less clear and the objective of this study is to determine the extent to which a growing tumor is able to insure its own success by the release of antigen into the circulation and whether immunological manipulations in this area can increase host resistance against the tumor. The first step will be to isolate tumor antigen, specific antibody, and produce "artificial" antigen-antibody complexes in vitro (and to determine the effect of these on tumor growth in vivo). Isotope labelled artificial complexes will be compared with their natural counterparts and will be used as models for developing techniques for isolation and identification of natural complexes from the serum of tumor-bearing animals. Natural complexes will be split at low pH and may serve as excellent sources of purified antigen and antibody. The rate of antigen production in vivo will be estimated and the rate and mechanism of its disposal will be determined. The effect on tumor growth of artificially loading tumor-bearing animals with antigen, antibody or complexes will be investigated. Resistance against tumor growth will also be induced or increased by immunizing macrophages with soluble antigen in vivo, transferring the immune cells to the intact animal. The ultimate goal of this study is to continue to look for new and rational models of immunotherapy based on better understanding of the antigen-antibody interactions involved in tumor growth.